<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>this</title>
</head>
<body>
<script type="text/javascript">
    function Parent(){
        this.a=1;
        this.b=[1,2,this.a];
        this.c={demo:5};
        this.show=function(){
            console.log(this.a,this.b,this.c.demo);
        }
    }
    function Child(){
        this.a=2;
        this.change=function(){
            this.b.push(this.a);
            this.a=this.b.length;
            this.c.demo=this.a++;
        }
    }
    Child.prototype=new Parent();
    var parent=new Parent();
    var child1=new Child();
    var child2=new Child();
    var child3=new Child();
    child1.a=11;
    child2.a=12;
    child3.a=13;
    parent.show();
    child1.show();
    child2.show();
    child1.change();
    child2.change();
    child3.change();
    parent.show();
    child1.show();
    child2.show();
    child3.show();

</script>

</body>
</html>